An essential cost factor in serial data communication systems is the number of pins required for transmitting and receiving clock signals. Another important cost criterion is the clock frequency on the communication connections between devices of a serial data communication system since the clock frequency determines the power consumption of the system.
Serial data communication systems with several devices often use a local clock generator or a high frequency clock signal from which required communication clocks are derived. However, if several different communication clocks for transmitting and receiving of data are required, the high frequency clock signal must have a frequency which is many times the number of the highest communication clock in order to allow to derive different communication clocks. Typically, the frequency must be 20 to 40 times higher than the highest communication clock. For example, for a communication clock of 5 MBaud, a high frequency clock signal with a frequency from 100 to 200 MHz is required. Such high frequencies must be guided over pins which generates a significant amount of power consumption.
It is also possible to provide a single device as a local clock generator for generating different communication clock signals for transmitting and receiving data. The communication clock signals may be guided to data communication devices which use it for serially transmitting and receiving signals from other data communication devices. However, this requires at least three connection lines from the local clock generator to the devices for guiding a transmit clock signal, a receive clock signal, and a control signal for controlling the communication. Therefore, the wiring is complex.